Evolution, Death and Nucleosynthesis of the First Stars

Transcription

1 First Stars IV, Kyoto, Japan, May 24, 2012 Alexander Heger Stan Woosley Ken Chen Pamela Vo Bernhad Müller Thomas Janka Candace Joggerst Evolution, Death and Nucleosynthesis of the First Stars

2 Motivation: A Brief History of the Universe

3 Cosmic Dark Age ` (after recombination) Hubble Deep Field Alexander Heger time What the Big Bang made (The primordial abundance pattern) Brian Fields (2002, priv. com.) (Pop III star yields) Heger & Woosley (2010) Frebel et al. (2005) What We Find Today (The solar abundance pattern) Lodders (2003)

4 Setting the Stage: Pre-Supernova Evolution and Nucleosynthesis (Recap)

5 Once formed, the evolution of a star is governed by gravity: continuing contraction to higher central densities and temperatures Evolution of central density and temperature of 15 MꙨ and 25 MꙨ stars

6 Nuclear Burning Stages

7 radiative envelope (blue giant) net nuclear energy generation (burning + neutrino losses) net nuclear energy loss (burning + neutrino losses) total mass of star (reduces by mass loss) convection semiconvection C shell burning C shell burning C burning (radiative) He burning H burning convective envelope (red super giant) burning Ne O O O Si O Si O shell burning

8 Explosive Nucleosynthesis in supernovae from massive stars Fuel Main Product Innermost r-process ejecta νp-process Si, O Ni 56 Secondary Product T (109 K) Time (s) Main Reaction - >10? 1 (n,γ), β iron group >4 0.1 (α,γ) O Si, S Cl, Ar, K, Ca O, Ne O, Mg, Ne Na, Al, P (γ,α) p-process 11 B, 19F, 138 La,180Ta ( γ,n) ν-process 5 16 O + 16O ( ν, ν ), ( ν, e-)

9 Ejected metals

10 Naoki Yoshida: stars massive stars very massive stars very very massive stars very very very massive stars very very very very massive stars very very very very very massive stars very very very very very very massive stars very very very very very very very massive stars very very very very very very very very massive stars

11 Beers Scale adopted from Beers and Christlieb

12 + stars that do not enter hydrostatic burning

13 Open Questions

14 ?

15 ?

16 Eta Car a really big star in our galaxy today

17 Mass Loss due to Giant Eruptions? Nathan Smith, 2007, First Stars III How do the most massive stars evolve? Reduced mass loss on the main sequence followed by LBV & giant eruptions? What are these eruptions? (physics, number, recurrence) When do they occur? (internal evolution stage?) How do we model these eruptions? Pulsational Pair-Instability Supernovae (PPSN)?

18 Initial Rotation of Massive Stars Pop I/II Pop III

19 Initial Rotation of Massive Stars Pop I/II Pop III

20 Mass Loss due to Critical Rotation ANGULAR MOMENTUM mass star disk How important is mass loss due to critical (or fast) rotation? How do we quantify mass loss and angular momentum loss? How does it effect our stellar models? (Langer, Meynet, Maeder, Hirschi,...)

21 (Yoon et al. 2012)

22 Nucleosynthesis in Low-Mass Core Collapse Supernovae

23 Low-Mass Pre-SN Structure z9.6

24 Explosion of Low-Mass SN 2D simulation with neutrino transport and core cooling Explosion driven by convection not SASI Explosion starts fast as accretion drops very rapidly Mueller, Janka, Heger (2012, in prep.) u8.1

25 n-rich Ejecta Low-Mass SN Mueller, Janka, Heger (2012, in prep.) -> May produce elements below 1st r-process peak

26 R-Process in Low-Mass SN r-precess initiated for explosion with a few times 0.1 B z9.6a

27 R-Process in Low-Mass SN r-precess initiated for explosion with a few times 0.1 B z9.6a

28 R-Process in Low-Mass SN r-precess initiated for explosion with a few times 0.1 B z9.6b

29 R-Process in Low-Mass SN r-precess initiated for explosion with a few times 0.1 B z9.6b

30 Impact of rotation on s-process element production in very-metal-poor massive stars. C Chiappini et al. Nature 472, (2011) doi: /nature10000

31 Supernova Progenitor Masses Presupernova stars for Type IIp and II-L Solid Line: Salpeter IMF with 16.5 MΘ cutoff Dotted Line: Salpeter IMF with 35 MΘ cutoff (Smartt 2009) Exclude stars with Minitial > 20 MΘ as Type IIP/IIL progenitors at 95% confidence level?

32 Nucleosynthesis in Massive Pop III Stars

33 Supernovae, Nucleosynthesis, & Mixing SN, no mixing SN + mixing

34 Pop III Nucleosynthesis Elemental Yields as a function of initial mass non-rotating stars 120 stellar masses complete reaction network normalized to Mg Mg yield (ejecta mass fraction) RESULTS: e.g., Production of 7Li by neutrino interaction in very compact stellar envelope! Heger & Woosley (2010)

35 What Can Nucleosynthesis Do for Us?

36

37

38 Reconstruction of the IMF find low-z halo stars (HERES, SEGUE, ) primordial stars form, nucleosynthesis ejected ejecta incorporated in low-z halo stars measure abundances (VLT, KECK, ) obtain IMF of population of progenitor stars Frebel, priv. com. (2007) compare abundances to primordial star nucleosynthesis library

39 25 solar mass star, Pop III 0.3 B, mildly mixed 8x10-6 solar masses iron Umeda & Nomoto, Nature, 422, 871, (2003)

40 Comparison to Observational Data The most iron-poor star The second most iron-poor star Heger & Woosley (2010) different explosion energies ~1/1000 solar metallicity stars

41 Fit to Caffau Star 10.6 MꙨ 0.9 B Vo et al. (2012 in prep)

42 Reconstruction of the IMF Vo et al. (2012 in prep)

43 Pair-Instability Supernovae

44 A Good Name? } PISN PCSN hypernovae pair production SNe PSN pulsational pair-instability SNe PPSN

45 Nucleosynthesis in Pair-Instability Supernovae

46 Initial mass: 150MꙨ

47 Initial mass: 250MꙨ

48 Initial mass: 150MꙨ

49 Initial mass: 250MꙨ

50 approximate l xp e E explosion energy / B Fe-rich Fe-poor

51 excess from Low neutron 22 CNO -> Ne in helium burning No extended stable period of carbon and oxygen burning where weak interactions might increase the neutron excess

52 Problem Pair-Instability Supernovae do not reproduce the abundances as observed in very metal poor halo stars!

53 Summary The IMF or the First Stars and hence how they come to pass still remains elusive without observational data Uncertainties in Fates of the First Stars largely come from uncertainties in their initial properties: mass, rotation, binarity Significant uncertainty also exists in the modeling of the stellar physics of primordial stars very massive stars in general, but particularly, as with all theory, if there is no experimental (observational) constrain Stellar forensics, determining abundance patterns of what the first stars left behind, may be our best tool in the near future (e.g., constraints on pair-sne)